User's Manual
PCS3_HD_v01.000-03
Confidential / Preliminary
Page 37 of 101
2013-10-21
PCS3 Hardware Interface Description
3.6 USB Interface
3.6.1
Reducing Power Consumption
While a USB connection is active, the module will never switch into SLEEP Mode. Only if the
USB interface is in Suspended state or Detached (i.e., VUSB_IN = 0) is the module able to
switch into SLEEP mode thereby saving power. There are two possibilities to enable power re-
duction mechanisms:
•
Recommended implementation of USB Suspend/Resume/Remote Wakeup:
The USB host should be able to bring its USB interface into the Suspended state as
described in the “Universal Serial Bus Specification Revision 2.0“
1
. For this functionality to
work, the VUSB_IN line should always be kept enabled. On incoming calls and other events
PCS3 will then generate a Remote Wakeup request to resume the USB host controller.
See also [5] (USB Specification Revision 2.0, Section 10.2.7, p.282):
"If USB System wishes to place the bus in the Suspended state, it commands the Host Con-
troller to stop all bus traffic, including SOFs. This causes all USB devices to enter the Sus-
pended state. In this state, the USB System may enable the Host Controller to respond to
bus wakeup events. This allows the Host Controller to respond to bus wakeup signaling to
restart the host system."
•
Implementation for legacy USB applications not supporting USB Suspend/Resume:
As an alternative to the regular USB suspend and resume mechanism it is possible to
employ the RING0 or WAKEUP line to wake up the host application in case of incoming
calls or events signalized by URCs while the USB interface is in Detached state (i.e.,
VUSB_IN = 0). Every wakeup event will force a new USB enumeration. Therefore, the
external application has to carefully consider the enumeration timings to avoid loosing any
signalled events. For details on this host wakeup functionality see Section 3.10.4.
1.
The specification is ready for download on http://www.usb.org/developers/docs/